typedef struct {
      Req_Head i_rh;             // request header
      unsigned char i_md;        // media descriptor-unused
      unsigned char _far *i_cb;  // pointer to control block
      unsigned int i_cblth;      // control block length
      unsigned int i_sect;       // start sector-unused
      unsigned char _far *i_vol; // volid pointer-unused
      } Ioctl_rp;

